Novel photographic products and processes

ABSTRACT

THE PRESENT INVENTION IS DIRECTED TO A SILVER DIFFUSION TRANSFER PHOTOGRAPHIC PROCESS PRINT-RECEIVING ELEMENT WHICH COMPRISES A COMMON SUPPORT CARRYING ON ONE SURFACE A PLURALITY OF LAYERS EACH OF WHICH COMPRISES METALLIC SULFIDE, METALLIC SELENIDE, COLLODIAL METAL, THIOOXALATE OR THIOACETAMIDE SILVER PRECIPITATING AGENTS DISPOSED IN A GELATIN, DEACTYLATED CHITIN OR SILICA MATRIX WHEREIN EACH SUCH LAYER COMPRISES A SUBSTANTIALLY CONSTANT CONCENTRATION OF SILVER PRECIPITATING AGENT PER UNIT AREA, AND A DECREASING CONCENTRATION, LAYER-WISE, IN THE DIRECTION OF THE SUPPORT; AND TO PHOTOGRAPHIC SILVER DIFFUSION TRANSFER PROCESSES EMPLOYING SUCH PRINT RECEIVING ELEMENT.

March 2, 1971 E. LAND NOVEL PHOTOGRAPHIC PRODUCTS AND PROCESSES OriginalFiled Dec. 9, 1959 /SUPPORT I .PHOTOSENSITIVE SILVER HAM-DE i/;/[/4-444;/EMULSON -'PROCESSING COMPOSITION MULTI-LAYER AGE-RECEIVING STRATUMWITH VARYI CONCENTRATIO F SILVER PRECIPITATING NUCL SUPPORT FIG.I

MULTl-LAYER IMAGE-RECEIVING ST UM WITH VARYING CONCENTRATION SILVERPRECIPITATING NUCLEI I---SPREADER SHEET A RUPTURABLE CONTAIN HOLDINGPROCESSING COMPOSI N PHOTOSENSITIVE SILVER HALIDE EMULSION MULTI-LAY ERIMAGE-RECEIVING STRATUM WITH VARYING CONCENTRATION OF SILVERPRECIPITATING NUCLEI SUPPORT I NVENT( )R 6M fb. 06am! BY E/wum (ma maATTORNEYS Tlnited States Patent OffiCE 3,567,442. Patented Mar. 2, 19713,567,442 NOVEL PHOTOGRAPHIC PRODUCTS AND PROCESSES Edwin Land,Cambridge, Mass., assignor to Polaroid Corporation, Cambridge, Mass.Continuation of application Ser. No. 858,454, Dec. 9, 1959. Thisapplication Mar. 10, 1967, Ser. No. 622,133 Int. Cl. G03c 5/54 US. CI.96-29 3 Claims ABSTRACT OF THE DISCLOSURE The present invention isdirected to a silver diffusion transfer photographic processprint-receiving element which comprises a common support carrying on onesurface a plurality of layers each of which comprises metallic sulfide,metallic selenide, colloidal metal, thiooxalate or thioacetamide silverprecipitating agents disposed in a gelatin, deacetylated chitin orsilica matrix wherein each such layer comprises a substantially constantconcentration of silver precipitating agent per unit area, and adecreasing concentration, layer-wise, in the direction of the support;and to photographic silver diffusion transfer processes employing suchprint receiving element.

This application is a continuation of my copending US. application Ser.No. 858,454, filed Dec. 9, 1959.

This invention relates to photographic products and processes for thefabrication and utilization of said products and more particularly tophotographic products usefulin diffusion-transfer processes wherein alatent image contained in an exposed silver halide emulsion is developedtherein and a soluble silver complex, obtained by reaction of theundeveloped silver halide of said emulsion with an appropriate silverhalide solvent, is transferred from said emulsion to an image-receivingelement to provide therein a reversed positive silver image of thelatent image, and to processes for the fabrication of said products.

A principal object of the present invention is to provide transferprocesses for the aforementioned type and products for utilizationtherein whereby positive prints are produced exhibiting enhanced qualityand stability.

A further object of the present invention is to provide improvedproducts particularly useful in the aforementioned diffusion-transferprocesses as print-receiving elements, each of said products comprisinga multilayer image-receiving stratum, wherein each layer of said stratumcontains a progressively increasing concentration of silverprecipitating nuclei in respect to the concentration of said nucleicontained in adjacent layers, positioned less distant from the surfaceof the print-receiving element in contact with a silver halidetransferring medium, to thereby produce dense positive silver images ofexcellent pictorial quality and improved stability.

A still further object of the present invention is to provide transferprocesses of the aforementioned type and products for utilizationtherein whereby silvering, due to surface precipitation of elementalsilver on a print-receiving element, is avoided.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the several steps and relation andorder of one or more of such steps with respect to each of the others,and the product possessing the features, properties and relation ofelements which are exemplified in the following detailed disclosure, andthe scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawing wherein:

FIG. 1 is a diagrammatic enlarged cross-sectional view illustrating theassociation of elements during one stage of the performance of atransfer process and showing as one of the elements an embodiment of thenovel print-receiving elements of the present invention, the thicknessof the various materials being exaggerated;

FIG. 2 is a diagrammatic enlarged cross-sectional view of one form ofthe novel print-receiving elements of the present invention; and

FIG. 3 is a diagrammatic enlarged cross-sectional view illustrating theassociation of elements during one stage of the performance of anothertransfer process.

The present invention comprehends improved diffusiontransfer reversalprocesses and products of the type Whereby a positive print is obtainedin a single step by suitably treating a silver halide emulsioncontaining a latent image with a processing liquid. Preferably, theprocessing liquid is in a viscous condition and is spread in a thin filmbetween the photosensitive element comprising a silver halide emulsionand a multilayer image-receiving element containing varyingconcentrations of silver precipitants. The processing compositiondevelops the latent image in the emulsion and forms a soluble complex,for example, a thiosulfate or a thiocyanate compleX, with undevelopedsilver halide. This soluble silver complex is transferred, at least inpart, by imbibition, to the print-receiving element and the silvercomponent thereof is precipitated in the multilayer image-receivingstratum of the print-receiving element to provide a reversed, positivesilver image of the latent image therein.

It has been proposed to use in the formation of silver transfer printsby the aforementioned processes such materials as, for example, themetallic sulfides and selenides, thiooxalates and thioacetamides,disclosed in US. Pat. No. 2,647,056, issued July 28, 1953 to Edwin H.Land. Examples of silver precipitating agents or nuclei of the preferredtype are the so-called heavy metal sulfides of zinc, chromium, gallium,iron, cadmium, cobalt, nickel, lead, antimony, bismuth, silver, cerium,arsenic, copper and rhodium and the selenides of lead, zinc, antimonyand nickel. Other precipitating agents have been proposed such as, forexample, the colloidal metals and specifically colloidal silver. The useof silver precipitating agents to aid in the reduction and precipitationof metallic silver from silver complex ions in the presence of a silverhalide developing agent in photographic diffusion-transfer reversalprocesses is well known to the art and does not per se constitute afeature of this invention.

Further, it has been proposed to use in the formation of silver transferprints by the previously-mentioned processes certain special matrices inwhich the silver precipitating agent is so dispersed as to effect acontrolled precipitation of the soluble silver complex, the chosenmatrix serving to receive and suitably aggregate the precipitated silverto produce therein positive images. Preferably the silver precipitatingagents are dispersed in a suitable matrix formed of particles,preferably colloidal in size, of a chemically inert, absorbent material.It is preferable that these particles have a relatively low coefficientof absorption for light as compared to silver and satisfactory examplesof materials of this type are: colloidal silica, such as silica aerogel,fullers earth, diatomaceous earth, kieselguhr, Wood flour, infusorialearth, bentonite, filter aids such as Celite and Super-Floss (tradenames of Johns-Manville Sales Corp, New York, N.Y., for diatomaceousearth filtration aids), and finely powdered glass, talc, mica or zincoxide. The use of a chemically inert, absorbent matrix to aid in theprecipitation of the soluble silver complex in photographicdiffusion-transfer reversal processes is Well known to the art and doesnot per se constitute a feature of this invention.

According to the present invention, the precipitation and aggregation ofsilver obtained by using silver precipitating agents, including theaforementioned materials, is greatly improved and expedited by providinga printreceiving element having a plurality of layers containing avarying concentration of silver precipitating agents, especially whereinthe concentration of silver precipitating nuclei progressively increasesas the distance of the respective layers from the external surface ofthe imagereceiving stratum increases.

It will be recognized that the concentration of silver precipitatingnuclei within one or more layers may remain constant or vary, that is,vary randomly or according to a prearranged distribution. In addition,the matrix of each layer may comprise, Where desired, a single componentor a mixture of components, and two or more layers may comprisedifferent matrices.

The novel print-receiving element is preferably fabricated bysuccessively applying to a suitable support the respective silverprecipitating nuclei-containing layers. The respective layers arepreferably dried prior to successive coating operations. The support maybe formed of a material such as, for example, paper, regeneratedcellulose, polyvinyl alcohol, cellulose ethers such as methyl cellulose,ethyl cellulose, or their derivatives, and other natural and syntheticgums and resins which will form continuous films and which arerelatively stable, mechani cally, in the presence of water and alkali.The supporting sheets are preferably opaque when a reflection print isdesired and transparent when a transparency is desired.

As previously noted, it is preferable that the respective layers bedried prior to successive coating operations. However, it must be notedthat even though the layers are deposited under dry conditions theinterface between contiguous layers may dissipate, particularly where acommon matrix material is used for the several layers.

One method of preparing the respective silver precipitatingagent-containing layers may comprise forming a dispersion of silverprecipitating agents by vacuum depositing, as for example, by cathodesputtering, an appropriate silver precipitating agent on a suitablematrix and blending the resulting product in a coating solvent.Processes of the aforementioned type are disclosed in the copending U.S.application of Edwin H. Land, ,Ser. No. 705,845, filed Dec. 30, 1957,abandoned and replaced by Ser. No. 249,922, filed Jan. 7, 1963, now U.S.Pat. No. 3,295,972, issued Jan. 3, 1967. The coating compositionscontaining the desired concentration of silver precipitating agents areprepared by dilution of the aforementioned blended product. Next, therespective coating compositions comprising progressively decreasingconcentrations of silver precipitating agents are successively coated ona suitable support. As previously mentioned, it is preferred that eachsuccessive layer be dried prior to succeeding coating operations.

An illustrative process for forming the novel printreceiving elements ofthe present invention is set out below.

A coating formulation is prepared by evaporating parts of silver onto400 parts of twenty mesh carboxymethyl cellulose powder. 5 parts of theresultant product are dissolved in 100 parts of an aqueous gelatincomposition containing 2% of gelatin and 2% deacetylated chitin.(Image-receiving layers containing deacetylated chitin are disclosed andclaimed in U.S. Pat. No. 3,087,815 issued Apr. 30, 1963 in the name ofWilliam H. Ryan and Elizabeth L. Yankowski.) A support comprising apolyvinyl butyral-coated baryta paper is coated with the aforementionedformulation. After the coating has dried, a second layer comprising theaforementioned formulation diluted in the ratio of 1 cc. to 9 cc. withthe aforementioned gelatin-deacetylated chitin composition is coated onthe exposed surface of the initial coating and dried.

Particularly desirable results are obtained when the silverprecipitating agents in the image-receiving layer are disposed in amatrix comprising a macroscopically continuous stratum comprisingsubmacroscopic agglom crates of minute particles of a suitablewater-insoluble, inorganic, preferably siliceous material, such, forexample, as silica aerogel. Suitable matrices of this type are disclosedin U.S. Pat. No. 2,698,237.

Other techniques for incorporating a silver precipitating agent, such asdissolving said agent in a solution of the matrix-forming material, mayalso be employed.

It will be recognized that the silver-receptive stratum of the presentinvention is so constituted as to provide an unusually vigorouselemental silver precipitating environment which causes the elementalsilver deposited therein, in comparison with the amount of silverdeveloped in the silver halide photosensitive layer, to possess veryhigh covering power, that is, opacity for given mass of reduced silver.

Especially suitable as silver precipitating agents are the metallicsulfides and selenides, these terms being understood to include theselenosulfides, the polysulfides, and the polyselenides. Preferred inthis group are the socalled heavy metal sulfides previously noted. Forbest results it is preferred to employ sulfides whose solubilityproducts in an aqueous medium at approximately 20 C. vary between 10-and 10 and especially the salts of zinc, cadmium and lead. Also suitableas precipitating agents are heavy metals such as silver, gold, platinum,palladium, and mercury, and in this category the noble metals arepreferred and are preferably provided in the matrix as colloidalparticles. The salts of these heavy metals, preferably the simpleinorganic and readily reducible salts such as silver nitrate, goldchloride and gold nitrate, are also useful as silver precipitatingagents. In some instances, the metals are introduced into the matricesas salts and then reduced in situ prior to the use of the receptionmaterial in the silver transfer process to give a layer whose silverprecipitating agent is a colloidal metal. Where the salts are relativelylightor heatsensitive, this reduction may be accomplished simply byexposing the silver precipitating layer to diffused light or to heat.Still other satisfactory silver precipitating agents are certain of thethio compounds, for example, dithiooxalate and its lead and zinccomplexes, potassium dithiooxalate and the lead and nickel complexesthereof, and thioacetamide. The silver precipitating agents as notedabove are provided in highly dispersed condition, preferably ascolloidal particles.

Where the silver precipitating agent is one or more of the heavy metalsulfides or selenides, it is preferable to prevent the diffusion andwandering of the sulfide or selenide ions, as the case may be, by alsoincluding, in the silver precipitating layers or in separate layersclosely adjacent thereto, at least one metallic salt which issubstantially more soluble in the processing agent than the heavy metalsulfide or selenide used as the silver precipitating agent and which isirreducible in the processing agent. This more soluble salt has, as itscation, a metal whose ion forms sulfides or selenides which aredifficultly soluble in the processing agent and which give up theirsulfide or selenide ions to silver by displacement. Accordingly, in thepresence of sulfide or selenide ions the metal ions of the more solublesalts have the effect of immediately precipitating the sulfide orselenide ions from solution. These more soluble or ion-capturing saltsmay be either soluble salts of any of the following metals: cadmium,cerium (ous), cobalt (ous), iron, lead, nickel, manganese, thorium, andtin. Satisfactory soluble and stable salts of the above metals may befound, for example, among the following groups of salts: the acetates,the nitrates, the borates, the chlorides, the sulfates, the hydroxides,the formates, the citrates, and the dithionates. The acetates andnitrates of zinc, cadmium, nickel, and lead are preferred. In general,it is also preferable to use the white or lightly colored salts althoughfor certain special purposes the more darkly colored salts may beemployed.

The previously mentioned ion-capturing salts may also serve a functionof improving the stability of the positive print provided they possess,in addition to the aforementioned characteristics, the requisitesspecified in US. Pat. No. 2,584,030 issued to Edwin H. Land. Forexample, if the ion-capturing salt is a salt of a metal which slowlyforms insoluble or slightly soluble metallic hydroxides with thehydroxyl ions in the alkaline processing liquid, it will suitablycontrol the alkalinity of the print-receiving element to substantially,if not totally, prevent the formation of undesirable developer stains.

The use of the novel print-receiving elements of the present inventionin the performance of a silver halide diffusion-transfer reversalprocess is illustrated diagrammatically in FIG. 1 wherein photosensitiveelement 12 comprises a support and a photosensitive silver halideemulsion layer 11; a layer 13 comprises a relatively vis cous processingcomposition; and print-receiving element 14 is one embodiment of thenovel print-receiving elements of the present invention. As shown, theprint-receiving element 14 comprises a suitable support 16 and amultilayer image-receiving stratum with a varying concentration ofsilver precipitants.

Multilayer image-receiving stratum 15 is formed by successively coatinga suitable support 16, for example of baryta paper, with a plurality ofsuspensions or sols containing progressively decreasing concentrationsof silver precipitating nuclei in suitable matrices. Each successivelayer is preferably permitted to dry preceding the coating of thesucceeding layer.

Liquid layer 13 may be obtained by spreading the processing composition,for example, in a manner disclosed in US. Pat. No. 2,647,056, issuedJuly 28, 1953 to Edwin H. Land. As disclosed in the aforementionedpatent, a rupturable container may be positioned between thephotosensitive element and the print-receiving element such that uponapplication of suitable pressure, for example by compression between apair of opposed, suitably gapped rollers, said container fracturesreleasing a liquid processing composition in contact with the transfersurfaces of each of said elements. The processing composition may be oneof the film-forming processing compositions disclosed in said patent. Itmay comprise, for example, a developing agent such as hydroquinone, analkali such as sodium hydroxide, a silver halide complexing agent suchas sodium thiosulfate, for forming a soluble silver complex withunexposed and undeveloped silver halide, and a high. molecular weight,film-forming, thickening agent such as sodium carboxymethyl cellulose.All these materials are preferably in an aqueous solution. The variousphotographic reagents are preferably contained in solution in theprocessing liquid prior to the spreading thereof as layer 13. However,it must be noted that they may be in whole or in part added to theprocessing liquid as it is spread between elements 12 and 14, saidreagents being so located on or adjacent to the surface of one or bothof said elements as to be dissolved by or otherwise interacted with theliquid composition when the latter wets said elements.

An illustration of a process for forming a positive image, in which asilver halide transfer takes place and in a which an embodiment of thenovel products of the present invention is used as a print-receivingelement in the performance of said process, is set out below.

A processing agent may be prepared which comprises:

Grams Water 1860 Sodium carboxymethyl cellulose 93 Sodium sulfite 78Sodium hydroxide 74.6 Sodium thiosulfate 14.5 Citric acid 38.5Hydroquinone 52 and is spread in a layer 13 between the coated surfaceof element 12 and a selectively exposed photosensitive silver halideemulsion 11. The lamination formed by the spreading of the processingagent in a layer 13 between elements 12 and 14 is kept intact forapproximately one-half to one and one-half minutes, preferably oneminute, and at the end of this time element 14 is stripped from element12. Element 14, when so stripped, carries a reversed positive print insilver of the subject matter of the latent image in emulsion 11. Thelayer 13 of the processing composition preferably adheres to emulsion 11and solidifies thereon.

Other materials may be substituted for those used in the foregoingprocess and the proportions may be varied to an appreciable extent. Forexample, the film-forming material in the processing agent which impartsthe desired viscosity to the latter may be any of the high molecularweight polymers which are stable to alkali and which are soluble inaqueous akaline solutions. For example, such other plastics ashydroxyethyl cellulose, polyvinyl alcohol, and the sodium salts ofpolymethacrylic acid and polyacrylic acid may be used. The plastic ispreferably contained in the agent in suflicient quantity to impart tothe composition a viscosity in excess of 1000 centipoises at atemperature of approximately 20 C. Preferably, the viscosity of theprocessing agent is of the order of 1000 to 200,000 centipoises.

Other developing agents may be used, for example, one of the following:p-aminophenol hydrochloride; bromohydroquinone; chlorohydroquinone;diaminophenol hydrochloride; diaminophenol dihydrochloride;toluhydroquinone; monomethyl-p-aminophenol sulfate; a mixture consistingby weight of /2 hydroquinone and /2 p-hydroxyphenylaminoacetic acid; anda mixture consisting by weight of A hydroquinone andp-hydroxyphenylaminoacetic acid.

To form the soluble silver complex, such other complex-formingsubstances as sodium thiocyanate, ammonium thiocyanate and ammonia maybe employed.

As illustrated diagrammatically in FIG. 3, another embodiment of theaforementioned difiusion-transfer processes comprises the relation ofelements wherein spreader sheet 19 is associated with a rupturablecontainer 20 holdmg at least a liquid photographic processingcomposition and a photosensitive silver halide emulsion layer 11 havingin superposed relation thereto a novel print-receiving element 15 of thepresent invention on a support 16.

Upon compression of the spreader sheet 19, rupturable container 20fractures, releasing its contents in a substantially uniform layerbetween spreader sheet 19 and a selectively exposed photosensitivesilverhalide emulsion layer 11. The processing composition permeatesemulsion layer 11, developing the latent image contained therein.Substantially simultaneously, undeveloped silver halide forms a solublesilver complex, by means of a silver halide solvent, as a function ofthe point-to-point degree of exposure of said photosensitive emulsion.An imagewise distribution of soluble silver complex is formed in theunexposed areas of the photosensitive emulsion and transferred, at leastin part, by imbibition, to print-receiving stratum 15, to form uponprecipitation of elemental silver therein, a reversed positive silverimage of the latent image. Subsequent to substantial precipitativedeposition of the image-forming elemental silver in stratum 15, photo- 7sensitive emulsion 11 may be dissociated from print-receiving stratum15, as by, for example, manual stripping.

In another form of the novel print-receiving elements of the presentinvention as illustrated in FIG. 2, it may be desirable to provide acoating on the silver precipitating layer 15 of a material, such as aplastic, more abrasionresistant than the matrix of the precipitatingnuclei-con taim'ng layers in order to protect the external surface ofthe image-receiving stratum. This overcoat of a plastic material mayalso serve as a layer which prevents adhesion of the film-formingprocessing composition 13 so that when element 17 is stripped from thephotosensitive element 12, at the completion of processing, thefilmforming processing composition layer 13 remains attached tophotosensitive element 12. An embodiment of this construction isillustrated in FIG. 2 wherein layer 18 is a suitable support, layer 15is a multilayer image-receiving stratum and there is applied over layer15 a thin coating of an abrasion-resistant coating 18 which may be, forexample, gum arabic, cellulose acetate hydrogen phthalate, polyvinylalcohol, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose,cellulose nitrate, sodium alginate, pectin, or poly-methacrylic acid.Layer 18 preferably has a thickness of the order of 1 to 3 microns,although if it is relatively water permeable, its thickness may beappreciably greater. Layer 18 may also contain one or more neutralizingagents which tend to improve the stability of the finished print. Aspreviously noted, the protective coating 18 may further serve as a layerfor minimizing the adhesion to the film-forming material of layer 13,particularly where said material is carboxymethyl cellulose.

Where desired, the solid film obtained from the filmforming processingiluid 13 may be caused to adhere to the print-receiving element 14 toprovide a protective coating thereon or caused to adhere tophotosensitive emulsion layer 11 rather than the print-receivingelement, as for example, according to the procedures disclosed in US.Pat. No. 2,647,056, issued July 28, 1953 to Edwin H. Land.

In addition to varying the concentration of the silver precipitatingagents, one may also vary the thicknesses of the individual layers ofsilver precipitating agents. It is also Within the scope of thisinvention to utilize different silver precipitating agents in two ormore of the layers and/or to utilize a mixture comprising two or moresilver precipitating agents in one or more of the layers.

The positive print is subject to several sources of instability whichstem, for example, from the oxidation of the developer in thehighlights, the discoloration of some of the unexhausted chemicalcomponents in the positive print by exposure to visible and near visibleradiation, the partial bleaching of the silver, and the interaction ofthe deposited silver with external sulfur and sulfides under conditionssuch that the structure of the precipitated silver is changed, usuallyto a yellow-to-brown form. This reduces the density and changes the toneof the positive transfer image. Diffusion-transfer processes utilizingthe single layer print-receiving structures of the prior art inherentlyresult in the deposition of a substantial quantity of the elementalsilver precipitate on or adjacent to an exposed surface of theprint-receiving element with the resultant proclivity of a substantialproportion of the positive image to adverse externally causeddeterioration. In addition, the deposition of the elemental silverprecipitate upon or in the surface area of the respectiveprint-receiving elements provides an undesirable silvering effect. Thenovel print-receiving structures of the present disclosure alleviate theaforementioned undesirable effects in that they provide a receptionelement wherein the tendency of the silver halide complex is to providea precipitate of elemental silver removed from the surface of saidelement.

In addition to the aforementioned increased stability afforded thepositive image, the novel print-receiving structures of the presentdisclosure provide image formation exhibiting decreased granularity andgraininess. The appearance of graininess in the transferred image isapparently not produced by the perception of individual submacroscopicgrains of deposited elemental silver, but rather the optical impressionof non-uniformity produced as a result of pattern effects whichthemselves appear to result from the irregular distribution of theelemental silver grains. When, as a result of the irregularity of thedisposition of silver grains, a substantial number of the respectivegrains are deposited in close proximity, the optical effect is that ofaggregation or clumping and, conversely, a deficiency in theconcentration of deposited grains per unit area reflects incompleteimage formation and definition. Inasmuch the print-receiving structuresof the present invention provide a vastly increased control of theelemental silver precipitation as well as the distribution of theprecipitating sites in the image-receiving stratum, the aforementionedeffects apparently due at least in part to random distribution of silverprecipitate in prior art structures are avoided.

Further, the novel print-receiving structures disclosed herein provideincreased resolving power, sharpness, density, contrast, covering power,and intensification resulting from an increased three-dimensional arrayof elemental silver precipitates per unit of viewed surface area.

The novel print-receiving elements of this invention provide severalother advantages. They are more stable during storage prior to use. Theimages formed therein do not exhibit image rub-off, which may occurwhere the image silver is precipitated on or close to the surface of theprint-receiving element. In addition, the use of layers of varyingconcentrations of silver precipitants makes it possible to selectivelyencourage the characteristics of the toe or shoulder portions of thecharacteristic curve of the image. This, in turn, permits the formationof images with characteristic curves which are smooth, long, straightline curves, thereby facilitating true copying of the resulting silvertransfer images, as well as of other images.

Since certain changes may be made in the above products and processeswithout departing from the scope of the invention herein involved, it isintended that all matter contained in the above description or shown inthe accompanying drawing shall be interpreted as illustrative ad not ina limiting sense.

What is claimed is:

1. In a process of forming a transfer image in silver which comprisesthe steps of developing an exposed silver halide emulsion with aprocessing composition comprising a silver halide developing agent and asilver halide solvent, forming an imagewise distribution of solublesilver complex in unexposed areas of said emulsion as a function of thepoint-to-point degree of exposure thereof, transferring from saidemulsion, at least in part, by imbibition, said imagewise distributionof soluble silver complex to a printrcceiving element in superposedrelationship with said emulsion so as to receive a depth-wise diffusionof said imagewise distribution and providing thereby a silver transferimage, and separating said print-receiving element from its superposedrelationship with said emulsion subsequent to substantial transfer imageformation, the im provement which comprises providing a visible silvertransfer image of improved stability comprising image silverprecipitated in each of at least two contiguous layers by transferringsaid imagewise distribution of said soluble silver complex to apreformed substantially photoinsensitive print-receiving elementcomprising a common support having on one surface thereof a plurality ofcontiguous layers, each of said layers comprising the same solid matrixselected from the group consisting of gelatin, deacetylated chitin and amacroscopically continuous matrix comprising submacroscopic agglomeratesof minute particles of water-insoluble, inorganic, chemically inert andabsorbent silica matrices and an effective concentration of the samesilver precipitating agent selected from the group consisting ofmetallic sulfide, metallic selenide, colloidal metal, thiooxalate andthioacetamide silver precipitating agents adapted to elfectprecipitation of said soluble silver complex, wherein each layer of saidplurality of layers comprises a substantially constant concentration ofsaid agent, per unit area, within said layer and a decreasingconcentration of silver precipitating agent, layerwise, as the distanceof the respective layer from the common support increases, and saidsilver halide emulsion, in superposed relationship, is in superpositionwith the layer of said plurality of layers positioned most distal fromsupport during said transfer of soluble silver complex from unexposedareas of said silver halide emulsion to said print-receiving element andsaid print-receiving element including said plurality of contiguouslayers is separated from said superposed relationship with said emulsionsubsequent to substantial transfer image formation.

2. As a photographic product, a substantially photoinsensitive diffusiontransfer print-receiving element which comprises a common support havingon one surface a plurality of contiguous layers, each of said layersincluding, dispersed in the same matrix selected from the groupconsisting of gelatin, deacetylated chitin and a macroscopicallycontinuous matrix comprising submacroscopic agglomerates of minuteparticles of Water-insoluble, chemically inert and absorbent silicamatrices, a substantially constant concentration of the same silverprecipitating agent selected from the group consisting of metallicsulfide, metallic selenide, colloidal metal, thiooxalate, and

thioacetamide silver precipitating agents, per unit area, within saidlayer, and a decreasing concentration of said silver precipitatingagent, layerwise, as the distance of the respective layer from thecommon support increases elfective to provide a visible silver transferimage comprising image silver precipitated in each of at least two saidcontiguous layers.

3. As a photographic product, a substantially photoinsensitive diffusiontransfer print-receiving element which comprises baryta paper carryingon one surface thereof, in order, first and second polymeric layers eachcomprising deacetylated chitin and gelatin and containing, as a silverprecipitating agent, a substantially constant concentration of silver,said second polymeric layer containing said silver at a concentrationper unit area of about oneninth of the concentration per unit areacontained in said first polymeric layer next adjacent said surface ofsaid baryta paper.

References Cited UNITED STATES PATENTS 2,563,342 8/1951 Land 6 2,774,66712/ 1956 Land et al 9629 3,313,625 4/1967 Ryan 9676 NORMAN G. TORCHIN,Primary Examiner J, GOODROW, Assistant Examiner US. Cl. X.R. 9676

